The present invention relates to a pump system and more particularly to an improved pump system for obtaining high pressure ratios at relatively low mass flow rates at relatively high efficiencies.
It is well known that in order for a conventional pump or compressor to operate efficiently, there are certain conditions which should be met. These conditions may be depicted by two dimensionless parameters known as:
1. Specific Speed EQU N.sub.s = N.sqroot.V.sub.1 /.DELTA.H.sup.3/4
2. specific Diameter EQU D.sub.s = D.DELTA.H .sup.1/4 /.sqroot.V.sub.1
where:
N = rpm PA1 V.sub.1 = Volume flow rate (ft.sup.3 /sec) PA1 D = Diameter of Impeller (ft) PA1 .DELTA.H = Adiabatic head (pumped) (ft)
The relationship of these parameters in terms of various designs of pumps and compressors may be expressed as a group of plots for radial design types, mixed flow design types and axial design types of compressors and pumps. From these graphical data, it becomes apparent that high efficiency of the device, a desirable design and operational quality, is only obtained over a specified region of the applicable curve.
In practice, however, pump and compressor performance in many cases is limited by the requirements set forth in the utilization of the available drive mechanisms. Thus, in most commercial applications using an electrical drive, the electrical motor speed is generally around 3400 rpm because of the use of 60 cps (Hertz) alternating current drives. In instances where large powers are contemplated, e.g. secondary oil reclamation, internal combustion engines (diesels or gas powered) drives may be employed and again there are practical limitations on speed of the power source, usually around 1800 to 3600 rpm.
In certain commercial operations such as reverse osmosis, boiler feed water systems, secondary oil recovery and oil field operations, chemical proportioning and mixing in chemical processing, fire fighting equipment, hydraulic mining and descaling and cleaning operations, to mention only a few operations, there is a need for fluid handling systems capable of generating a relatively high pressure flow at a relatively low volume flow rate, for example 60 gallons per minute at 500 psi.
As is known in the pump art, for a given fluid system the output pressure of the pump is a function of the square of the impeller tip velocity times the density of the fluid divided by 2g per stage. Thus, to provide the relatively high pressure, a substantial impeller tip speed is needed. The tip velocity is, as a practical matter, related to the rpm of the power source. Thus, some mechanism must be provided to obtain the high velocity tip speed needed to produce the desired pressure.
One possible approach is to use an impeller of a sufficient diameter to produce the desired tip speed for the power source. Calculations show that relatively large impeller diameters will be needed with accompanying relatively high disc friction resulting in poor efficiency, i.e. far greater horse power than for other systems. Thus, one of the principal problems for relatively high pressure and low flow rate systems is achieving the impeller tip speed needed from a power source whose rpm is in the range of 1800 to 3400 rpm due to the nature of the power source while achieving an acceptable efficiency for the system.